Interlaced cathode ray tube displays have been popular in the past compared with non-interlaced CRT displays because they required slower circuits. Although circuit technology has improved so that non-interlaced CRT displays are technically feasible, interlaced displays will remain popular for some time because they use slower and therefore cheaper circuits.
For a given video data rate, interlaced display exhibit less flicker than non-interlaced displays, their shorter-persistence, more efficient phosphors also resulting in brighter displays. Nevertheless, interlaced displays can suffer from flicker and various proposals have been made to reduce flicker. U.S. Pat. No. 4,521,774 describes an arrangement in which control logic selects the field scan in which a particular picture element (pixel or pel) is to be displayed, the selection being made such that pel imbalance between the two fields is minimized. British Patent Specification No. 2 004 716 describes a technique for subjectively reducing the flicker of a bright area on the display by introducing bright points on adjacent scan lines.
The articles in the IBM Technical disclosure Bulletin at page 1675, Vol 21 No. 4 (September 1978), pages 1673 and 1674, Vol 21 No. 4 (September 1978), pages 1704 to 1706, Vol 23 No. 4 (September 1980), and pages 1548 and 1549, Vol 20 No. 4 (September 1977) all describe techniques for reducing flicker.
It is thus well recognized that flicker in an interlaced display can be reduced by equalizing the number of pels (or bright areas) on the two fields of the interlace. However the known techniques either require complicated logic or other circuit arrangements, and/or are limited in their application, that is to alphanumeric displays or graphic displays or even to a particular character font design.